The simplest galvanic apparatus consists of a set of tumblers, containing water slightly mixed with nitric or sulphuric acid, which are connected by bent wires with a piece of zinc at one end, and a piece of copper at the other; connect the tumblers by placing these in them all in the same order - one metal in the first and last, and both metals in each intermediate one : - touching the first copper and the last zinc with the fingers will occasion a shock.
The pile is made thus: Take twenty or thirty pieces of zinc, each as large as a penny. Get as many pieces of copper about the same size, and also as many pieces of paper or cloth, which are to be dipped in a solution of salt and water. In building up the pile, place zinc, paper, copper, etc, constantly in the same order until the whole be finished. The sides of the pile may be supported with rods of glass, or varnished wood, fixed in the board on which it stands. The following experiments may then be performed : Having wet both hands, touch the lower part of the pile with one hand, and the upper part with the-other; a slight shock of electricity will be felt as often as one hand is removed. If the hand be brought back, a similar shock will be felt Put a basin of water near the pile, and put the left hand into it. holding a wire, the one end of which touches the top of the battery or pile ; then put the end of a silver spoon between the lip and the gum, and with the other end of the spoon touch the lower part of the pile; a strong shock is felt in the gum and in the hand. Take the left hand from the water, but still keep hold of the wire, and then perform the last experiment in the same manner, and a shock will be felt in the gum only. Hold a Silver spoon in one hand, and touch with it the battery at the lower part, then touch the upper part with the tongue, the bitter taste is extreme. In performing the above experiments, if, instead of the two ends of the pile, the one end and the middle of it be touched, the sensations will not be nearly so strong.
The Galvanic trough is a very powerful apparatus ; it is composed of zinc and copper plates placed in pairs, so that all those of one metal lie toward the same end. The end plates have connecting wires; and when the trough is filled with water, impregnated with nitric or muriatic, acid, and the points of the wires brought together, the action is remarkably powerful; any number of troughs may be united and made to act at once. In this way substances have been decomposed on which the strongest fires had no effect.
Modern research has considerably augmented our knowledge of Galvanism. It was, after some time, discovered that the efficiency of a Galvanic Circle depends on it3 being formed of three bodies, two of which have a powerful effect on each other, but neither of them, if possible, any on the third. Hence perfectly pure zinc, or (what answers extremely well) zinc amalgamated with mercury, platina, and dilute acid ; or charcoal, zinc, and acid; form batteries which are very effective, and which from their long-continued actions are called constant batteries; indeed, the zinc in them is not at all acted upon by the acid in which it is immersed, unless when connected with the platina, etc, by means of a wire or some other conductor, and then only to an extent proportioned to the goodness of the conductor which connects them.
Galvanic action is now applied to a very interesting and useful purpose, which is called the Electrotype process. This enables us with great facility, and the most perfect exactness, to copy medals, engraved copperplates, etc, and to cover almost any substance with gold, silver, copper, etc. In its simplest form it may be illustrated by a small Galvanic battery, consisting of a vessel of un-glazed porcelain, within which is a piece of zinc immersed in dilute sulphuric acid, and outside of it a plate of copper immersed in a solution of blue vitriol (sulphate of copper): when the zinc and copper are connected together by a wire, etc, the former will be gradually dissolved, and the latter covered with fine copper deposited from the blue vitriol.
The experiment will be more perfect when a generating cell (a constant battery) and a decomposing cell are used. Let us suppose the generating cell to consist of amalgamated zinc, platina, and dilute sulphuric acid; and the generating cell to be a vessel containing a solution of blue vitriol, in which a plate of copper and the modal intended to be copied are immersed, without being in contact. When the zinc of the generating cell is connected with the medal, and its platina with the plate of copper, the medal will in a few hours be covered with a plate of pure copper, whose thickness will depend on the time used in forming it, etc, and which being removed from the medal, and placed instead of it in the generating cell, will constitute a matrix, and be covered with copper, thus affording a copy of the medal, than which nothing can be more exact. The same matrix will, it is evident, be sufficient for the production of an indefinite number of copies.